1. Field of the Invention
The present invention relates to a method of manufacturing a photoelectric conversion apparatus including a MOS transistor.
2. Description of the Related Art
A photoelectric conversion apparatus is used in an image capturing apparatus such as a digital still camera or a video camcorder, and demand for this is increasing. Especially in recent years, as for the photoelectric conversion apparatus used in the digital still camera, a large size such as an APS-C size or a 35-mm film size is becoming widely used. MOS photoelectric conversion apparatuses are used as these photoelectric conversion apparatuses. In the MOS photoelectric conversion apparatuses, it is necessary to reduce noise generated in pixel circuit sections.
A change in density level called shading may occur in the output signal of a photoelectric conversion apparatus. An optical charge generated upon incidence of light on a photoelectric conversion element is converted into a voltage, and becomes an electrical signal. For the electrical signal as a voltage, an electrical signal component is added to the reference potential of a semiconductor substrate. For this reason, when the reference potential of the semiconductor takes different values depending on positions within an imaging area, the output signal of the photoelectric conversion apparatus takes different values accordingly even if the intensity of light entering the photoelectric conversion apparatus is constant. As a result, the change in density level which appears in the output image of the photoelectric conversion apparatus is called shading. In the case of a sensor having an imaging area of a large size demand of which is increasing in recent years as described above, shading greatly impairs the performance of the sensor. As a method of reducing this shading, Japanese Patent Laid-Open No. 2006-073737 discloses a method of providing a well contact for supplying a reference voltage to the common well of a pixel section.